Prop Pitch & Slip

Theoretical top end from RPM and pitch, and how much of that you're actually losing to slip once GPS speed is in the mix.

RPM · PITCH · GEAR

Prop slip is the gap between what your prop's pitch says you should be doing and what your GPS actually shows. Some slip is normal and necessary — a prop with zero slip wouldn't be generating any thrust. The question is whether your slip is in a healthy range or telling you something's wrong with prop selection or boat loading.

Inputs

Engine RPM 5500

Gear ratio 2.0:1

Prop pitch 17 in

Actual GPS speed (optional) 32 mph

Formula: theoretical mph = (prop RPM × pitch in) ÷ 1056, where prop RPM = engine RPM ÷ gear ratio. Set actual speed to 0 to hide the slip readout.

Result

49.3

theoretical mph, zero slip

Prop shaft RPM2750

Slip35.1%

Healthy slip on a loaded fishing boat is usually 10–20%. Higher than that often means a prop pitched too high, too much cup, or a hull that's overloaded/squatting.